Re: [HACKERS] Big IN() clauses etc : feature proposal

Hi, PFC,

PFC wrote:

> You need to do some processing to know how many rows the function
> would return.
> Often, this processing will be repeated in the function itself.
> Sometimes it's very simple (ie. the function will RETURN NEXT each
> element in an array, you know the array length...)
> Sometimes, for functions returning few rows, it might be faster to
> compute the entire result set in the cost estimator.

I know, but we only have to estmiate the number of rows to give a hint
to the query planner, so we can use lots of simplifications.

E. G. for generate_series we return ($2-$1)/$3, and for some functions
even constant estimates will be good enough.

> - please execute me and store my results in a temporary storage,
> count the rows returned, and plan the outer query accordingly

That's an interesting idea.

Markus

--
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf. | Software Development GIS

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